Acquisition - Summary of Cash Consideration Paid, and Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jul. 03, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Bargain purchase gain		$ 1,276
First Eastern Bankshares Corporation [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	$ 2,951
Loans held for sale	26,659
Loans	31,306
Mortgage servicing rights	6,216
Premises and equipment	3,100
Core deposit intangible	118
Other assets	1,991
Deposits	(41,790)
Federal Home Loan Bank advances	(13,188)
Other liabilities	(2,005)
Total identifiable net assets	15,358
Cash consideration paid to seller	14,082
Bargain purchase gain	1,276
First Eastern Bankshares Corporation [Member] | As Acquired [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	2,951
Loans held for sale	26,209
Loans	30,824
Mortgage servicing rights	4,396
Premises and equipment	1,566
Goodwill	789
Other assets	2,046
Deposits	(41,737)
Federal Home Loan Bank advances	(13,128)
Other liabilities	(1,917)
Total identifiable net assets	11,999
First Eastern Bankshares Corporation [Member] | Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Loans held for sale	450
Loans	482
Mortgage servicing rights	1,820
Premises and equipment	1,534
Core deposit intangible	118
Goodwill	(789)
Other assets	(55)
Deposits	(53)
Federal Home Loan Bank advances	(60)
Other liabilities	(88)
Total identifiable net assets	$ 3,359